The 2011 West Nile disease outbreak in Sardinia region, Italy.

In 2011, strains of West Nile Virus (WNV) belonging to lineage 1 spread for the first time in Sardinia region (Italy). In contrast to previous WNV Italian incursion, the strains were found in Culex modestus and, more surprisingly, they were able to cause severe clinical signs in the affected birds. Based on the partial sequence of the NS3 encoding gene, the Sardinian WNV strains demonstrated a high similarity with the other WNV strains recently detected in the Mediterranean Basin. Nonetheless, the 2011 Sardinian sequences were grouped in a distinct sub-cluster. Both the NS3-249P and NS3-249T genotypes were detected in the Sardinian outbreaks confirming that the co-circulation of different genotypes in the affected population might be common for WNV as for many RNA viruses. No association, however, was observed between virulence and viral genotype.